Composition and Annealing Effects on the Mechanical Properties of Superelastic Thin Film Nickel Titanium

摘要

This work examines the influence of annealing temperature on the transformation temperatures, stress necessary to induce martensite (σ_(AM)), and the Young's modulus of superelastic NiTi of two different compositions--47.5 at.% Ni and 50.5 at.% Ni. The films were sputter deposited, crystallized, and annealed for two hours at three different temperatures of 400℃, 500℃, and 600℃. Isothermal tensile tests at the austenite finish temperature (A_f) were performed for evaluating the mechanical response. For the 47.5 at.% Ni film, increasing the annealing temperature from 400℃ to 500℃ decreased σ_(AM) by 55 MPa, while the film annealed at 600℃ failed to demonstrate complete superelastic behavior. For the 50.5 at.% Ni film, increasing the annealing temperature from 400℃ to 600℃ decreased σ_(AM) by 138 MPa. Results were explained using the transformation temperatures and the Clausius-Clapeyron relationship.